The Evolved Packet System (EPS) of the 3rd Generation Partnership Project (3GPP) is composed by the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), the Mobility Management Entity (MME), the Serving Gateway (S-GW), the Packet Data Network Gateway (P-GW), the Home Subscriber Server (HSS), the 3GPP Authentication Authorization Accounting server (3GPP AAA server), the Policy and Charging Rules Function (PCRF) and other support nodes.
FIG. 1 is a schematic diagram showing the system architecture of EPS in the related art, wherein MME is responsible for related work of the control plane such as mobility management, processing of non access stratum signaling and management of the user's mobility management context; S-GW is access gateway equipment connected to E-UTRAN and is used to forward data between E-UTRAN and P-GW and is responsible for caching paging waiting data; P-GW is a border gateway between EPS and the Packet Data Network (PDN) and is in charge of functions such as access of PDN and forwarding data and so on between EPS and PDN.
EPS supports interconnection with the non-3GPP network and implements the interconnection with the non-3GPP network by S2a/b/c interfaces. The non-3GPP network includes a trusted non-3GPP network and an untrusted non-3GPP network. Internet Protocol (IP) access of the trusted non-3GPP network can be directly connected with P-GW by the S2a interface; IP access of the untrusted non-3GPP network needs to be connected with P-GW through the (Evolved Packet Data Gateway (ePDG), wherein ePDG and P-GW are connected by the S2b interface.
If an EPS system supports Policy and Charging Control (PCC), then PCRF makes policy and charging rules; PCRF is connected to an IP service network of the operator through a receiving interface Rx to obtain service information. In addition, PCRF is connected with gateway equipment in a network by the Gx/Gxa/Gxc interface and is in charge of initiating establishment of the IP bearer, ensuring Quality of Service (QoS) of service data, and performing charging control, wherein Policy and Charging Enforcement Function (PCEF) is located at P-GW, and PCRF and P-GW exchange information through a Gx interface. When the interface between P-GW and S-GW is based on Proxy Mobile IP (PMIP), a Bearer Binding and Even Report Function (BBERF) exists in S-GW, and information between S-GW and PCRF is exchanged via a Gxc interface. When UE accesses the untrusted non-3GPP network, there is also a BBERF residing in S-GW, and the access gateway of the trusted non-3GPP network and PCRF exchange information through the Gxc interface. When User Equipment (UE) is roaming, an interface between the home PCRF and the visited PCRF is an S9 interface, and meanwhile an Application Function (AF) providing services for UE is located at a service network and sends service information for generating the PCC policy to PCRF through an Rx interface.
In the related art, the protocols applied in the PCC architecture are Diameter application protocols developed on the basis of the Diameter Base protocol; for example, the application protocol applied in a Gx interface, the application protocol applied in an Rx interface, the application protocol applied in a Gxx interface (including Gxa and Gxc interfaces) and the application protocol applied in a roaming interface S9 and so on. These application protocols define messages, commands and Attribute Value Pairs (AVP) and so on for PCC. The Diameter sessions established by these protocols can be respectively called as the Gx session, the gateway control session (Gxx session), the Rx session and the S9 session. The various function entities of PCC perform policy and charging control for the PDN connection established for UE accessing the network by these sessions. One IP connection from UE to PDN is generally called as one IP Connectivity Access Network (IP-CAN) session. One important operation enforced by PCRF is to link the Gx session, Gxx session and S9 session for performing policy and charging control to an identical IP-CAN session. The linking operation is performed in the process of establishing and modifying an IP-CAN session. In this text, the above Diameter sessions are called as the policy and charging control session.
FIG. 2 is a flowchart showing initial attachment where UE accesses EPS through E-UTRAN and establishes a PDN connection (i.e., an IP-CAN session), wherein a PMIPv6 protocol is applied between S-GW and P-GW. The procedure illustrated in FIG. 2 comprises the following steps.
Step S201: UE sends an attachment request message to eNodeB (Evolved Node B, that is, base station, called eNB for short) to request for accessing EPS.
Step S202: eNodeB sends the attachment request message to MME.
Step S203: the network authenticates UE and starts Non Access Stratum (NAS) security encryption protection.
Step S204: MME interacts with HSS to enforce a location update procedure after authenticating UE.
Step S205: MME selects P-GW for UE according to a default Access Point Name (APN) subscribed by the user and selects S-GW, and MME sends an establishment default bearer request message to the selected S-GW; “APN” represents “default APN” hereinafter in the absence of ambiguity.
Step S206: BBERF located at S-GW sends a gateway Control session establishment indication message to PCRF, wherein the gateway control session establishment indication message includes a user identity Network Access Identifier (NAI), a PDN identity APN and bearer attributes of the current access network and so on; the gateway control session (Gxx session) that this gateway control session establishment indication message makes a request for establishing is represented as Gxx session1;
wherein the bearer attributes of the access network includes: an IP-CAN type and a BBERF address; in addition, the bearer attributes of the access network can further include a Radio Access Technology (RAT) type.
Step S207: PCRF obtains user subscription information according to the user identity NAI and PDN identity APN, thereby making policies according to the user subscription information, network policies and bearer attributes of the current access network (including the IP-CAN type, or the IP-CAN type and the RAT type), and at this time the policy made by PCRF is a default policy for the user accessing this APN, including PCC rules, QoS rules and event triggers;
PCRF returns a gateway control session establishment acknowledgement message to BBERF and sends the made QoS rules and event triggers to BBERF; BBERF installs and enforces QoS rules and event triggers.
Step S208: S-GW sends a proxy binding update message to P-GW selected by MME in step S205, wherein the proxy binding update message includes the user identity NAI, PDN identity APN and bearer attributes of the access network (including the IP-CAN type, or the IP-CAN type and the RAT type).
Step S209: P-GW allocates an IP address for a PDN connection that is requested to establish for UE access, wherein the IP address is represented as IP Address1;
PCEF located at P-GW sends an IP-CAN session establishment indication message to PCRF, wherein this IP-CAN session establishment indication message includes the user identity NAI, PDN identity APN, IP Address1 and bearer attributes of the access network (including the IP-CAN type, or the IP-CAN type and the RAT type); the bearer attributes of the access network in this IP-CAN session establishment indication message are obtained in Step S208; and Gx session that this IP-CAN session establishment indication message requests to establish is represented as Gx session 1.
Step S210: PCRF links Gxx session1 to Gx session1 according to NAI and APN, that is, Gxx session1 and Gx session1 are used to perform policy and charging control to a PDN connection (i.e., the IP-CAN session) that UE requests to establish.
Step S211: PCRF returns an IP-CAN session establishment acknowledgement message to PCEF and sends the PCC rules and event triggers made in Step S207 to PCEF; the PCEF installs and enforces PCC rules and event triggers;
PCRF may modify the PCC rules and QoS rules according to the bearer attributes of the access network reported in Step S209, and at this time PCRF will send the modified PCC rules and QoS rules respectively to PCEF and BBERF for update.
Step S212: P-GW returns a proxy binding acknowledgement message including the IP Address1 to S-GW.
Step S213: S-GW returns an establishment default bearer reply message including the IP Address1 to MME.
Step S214: MME returns an attachment acceptance message including the IP Address1 to eNodeB.
Step S215: eNodeB returns an attachment acceptance message including the IP Address1 to UE.
Step S216: UE sends an attachment completion message to eNodeB.
Step S217: eNodeB sends an attachment completion message to MME.
Step S218: MME and S-GW perform an interaction procedure for updating the bearer.
Step S219: MME acquires that UE can access non-3GPP according to the user subscription information, and therefore sends the address of P-GW selected for UE establishing the PDN connection (i.e., the IP-CAN session) to HSS; HSS returns a reply message after storing this P-GW address.
According to the procedure illustrated in FIG. 2, UE has established a PDN connection (i.e., the IP-CAN session) to default APN; and thereafter UE can access dedicated services through this connection, and PCRF will make PCC rules and QoS rules according to information such as service features, user subscription information, network policies and bearer attributes of the access network and so on. Since linking is performed in Step S210, PCRF can send PCC rules to PCEF by Gx session1 and send QoS rules to BBERF by Gxx session1. When BBERF requests new QoS rules or modifies QoS rules through Gxx session1, PCRF will also make corresponding PCC rules or modify corresponding PCC rules and send the PCC rules to PCEF by Gx session1, and vice versa.
When inter-system handover or inter-S-GW handover (i.e., BBERF relocation) takes place in UE, PCRF needs to enforce a new linking operation.
FIG. 3 is a flowchart showing that UE switches from E-UTRAN to a trusted non-3GPP access system after accessing to EPS using the procedure illustrated in FIG. 2, wherein through non-3GPP access, PMIPv6 protocol is applied between trusted non-3GPP access gateway and P-GW. The procedure illustrated in FIG. 3 comprises the following steps.
Step S301: UE establishes a PDN connection (i.e., an IP-CAN session) through 3GPP access, wherein there is a PMIPv6 tunnel between S-GW and P-GW.
Step S302: UE finds a trusted non-3GPP access system and decides handover of the current session from 3GPP access to this trusted non-3GPP access system.
Step S303: UE, the trusted non-3GPP access gateway and HSS/AAA perform an Extensible Authentication Protocol (EAP) authentication process, in which HSS/AAA returns the address of P-GW selected when the access of UE is based on 3GPP to the trusted non-3GPP access gateway.
Step S304: the layer 3 attachment procedure specific to non-3GPP access is triggered after authentication and authorization succeed; in this process, UE indicates the network that UE has the IP address maintaining capacity.
Step S305: BBERF located at the trusted non-3GPP access gateway sends a gateway control session establishment indication message including the user identity NAI, PDN identity APN and bearer attributes of the current access network (including the new IP-CAN type, new RAT type and new BBERF address) to PCRF; the gateway control session (Gxx session) that this message requests to establish is represented as Gxx session 2.
Step S306: PCRF links Gxx session2 to Gx session1 established in the procedure illustrated in FIG. 2 according to the user identity NAI and the PDN identity APN.
Step S307: PCRF makes QoS rules and event triggers, which include the policy made by PCRF for UE when UE accesses dedicated services through 3GPP access, for UE during non-3GPP access according to user subscription information, network policies and bearer attributes of the current access network;
PCRF sends the above QoS rules and event triggers to BBERF by a gateway control session establishment acknowledgement message; BBERF installs and enforces the QoS rules and event triggers; the trusted non-3GPP access gateway enforces a specific non-3GPP access procedure for resource reservation.
Step S308: the trusted non-3GPP access gateway sends a proxy binding update message including the user identity NAI, PDN identity APN and bearer attributes of the current access network (including the IP-CAN type, or the IP-CAN type and RAT type) to corresponding P-GW according to a P-GW address obtained in Step 303.
Step S309: P-GW allocates an IP address (IP Address1) used by UE during 3GPP access for UE according to the user identity NAI and PDN identity APN so as to maintain IP address unchanged, thereby ensuring continuity of services;
PCEF located at P-GW sends an IP-CAN session modification indication message including bearer attributes of the new access network obtained in step S308 to PCRF; this message modifies Gx session1 established in the procedure illustrated in FIG. 2.
Step S310: PCRF determines that the handover (i.e., handover from 3GPP to non-3GPP) occurs in the tunnel of a PDN connection (i.e., IP-CAN session) established by UE, and therefore PCRF modifies PCC rules for a reestablished PDN connection (i.e., IP-CAN session) according to bearer attributes of the new access network and returns the modified PCC rules to PCEF by an IP-CAN session modification acknowledgement message for update.
Step S311: P-GW returns a proxy binding acknowledgement message including IP Address1 to the trusted non-3GPP access network.
Step S312: the trusted non-3GPP access network returns a layer 3 attachment completion message including IP Address1 to UE.
Step S313: UE performs handover on the PDN connection from 3GPP access to trusted non-3GPP access, wherein there is a PMIPv6 tunnel between the trusted non-3GPP access gateway and P-GW (this PMIPv6 tunnel is established by Steps S308 and S311); the services accessed by UE during 3GPP access can be continuously accessed.
It can be seen from the procedure illustrated in FIG. 3 that PCRF links a new gateway control session (Gxx session) to an established PDN connection (IP-CAN session) according to the user identity NAI and PDN identity APN in Step S306, so that PCRF can update the policy made by PCRF for UE when UE accesses a 3GPP system according to bearer attributes of the new access network and then send the policy to new BBERF by this new gateway control session (Gxx session), thereby ensuring that a non-3GPP access system has performed resource reservation for the services which UE previously accessed before handover occurring in the PMIPv6 tunnel (i.e., before Step S308), accelerating the handover speed and improving user experience.
However, not all UEs can implement a handover procedure (i.e., maintaining IP address unchanged). When a network cannot determine whether UE has a network mobility capacity (i.e., IP address maintaining capacity), the P-GW would decide whether to allocate a new IP address (i.e., establishing a new PDN connection) for UE or maintain the IP address unchanged (i.e., handover of the established PDN connection). However, this decision is made by P-GW after receiving the proxy binding update message sent by the trusted non-3GPP access network gateway. At that time, PCRF has made a decision to link a new gateway control session (Gxx session) to an existing PDN connection (i.e., PCRF has made a decision of handover). If at this time P-GW decides to establish a new PDN connection rather than perform handover, it necessarily results in inconsistency of the policy sent by PCRF with the decision of P-GW, thereby causing occurrence of the error. The method for solving this problem in the related art is as follows.
(1) When the access gateway cannot determine whether UE has a network mobility capacity, an deferred linking indication is included in the gateway control session establishment indication message sent by BBERF located at the access gateway to PCRF, and PCRF does not immediately link the established gateway control session (Gxx session) (i.e., Gxx session2 in FIG. 3) to the existing PDN connection (IP-CAN) after receiving the deferred linking indication.
(2) If P-GW decides to perform handover, PCEF located at P-GW sends an IP-CAN session modification indication message to PCRF for modifying the established Gx session (i.e., Gx session1 in FIG. 3), and at this time PCRF links a newly established gateway control session (Gxx session) (i.e., Gxx session2) to the established PDN connection (IP-CAN session) (i.e., linking Gxx session2 to Gx session1);
(3) if P-GW decides to newly establish a PDN connection (IP-CAN session) instead of not performing handover, P-GW allocates a new IP address (represented as IP Address2) for UE; PCEF located at P-GW sends an IP-CAN session establishment indication message including the user identity NAI, PDN identity APN and IP Address2 to PCRF for requesting to establish a new Gx session (represented as Gx session2); at this time PCRF decides to link the newly established gateway control session (Gxx session) to the newly established Gx session. In this case, the dedicated services which UE previously accessed through 3GPP access will be interrupted, and UE needs to reinitiates a service request and PCRF remakes a policy for UE.
The above method that does not immediately link the gateway control session to the existing PDN connection (IP-CAN) is called as deferred linking.
Only the method for implementing deferred linking of the policy and charging control session in non-roaming scenarios was discussed in the related art. The related art does not involve the roaming scenarios.
There are two kinds of roaming architectures in EPS: the first one is home routed and the second one is local breakout. FIG. 4 is a diagram showing the home routed EPS roaming architecture in the related art. As illustrated in FIG. 4, P-GW is in home network and an IP service is provided by the home network operator (i.e., AF is in home network). FIG. 5 is a diagram showing the local breakout EPS roaming architecture in the related art. As illustrated in FIG. 5, P-GW is in the local network and an LP service can be provided by the home network operator (i.e., AF is at home network) or by the visited network operator (i.e., AF is in the visited network). As for different roaming scenarios, the procedures of PCC are different and the functions enforced by the PCC network element are also different.
Currently, in the scheme of implementing an S9 roaming interface, Visited PCRF (vPCRF) terminates the Gx sessions and gateway control sessions (Gxx sessions) of all IP-CAN sessions established by UE that exist in the visited network, that is, the gateway control session (Gxx session) and the Gx session would not be sent to the Home PCRF (hPCRF), but a S9 session is established between vPCRF and hPCRF, and this S9 session is used to transmit the information on the Gx sessions and the gateway control sessions (Gxx session) of all IP-CAN sessions. However, vPCRF does not terminate Rx sessions of all IP-CAN session in the visited network, but only forwards messages of Rx sessions to the home PCRF and takes vPCRF as one proxy. There may be a plurality of subsessions (called as S9 subsession) in one S9 session, and each subsession is used to transmit information on Gx and Gxx sessions of one IP-CAN session.
To sum up, due to complexity of EPS roaming scenarios and complexity of deferred linking of policy and charging control sessions itself in roaming scenarios, there are difficulties in implementing a method for implementing deferred linking of policy and charging control sessions in the roaming scenarios and the policy and charging control thereon, and there has not had a corresponding solution in the related art.